Coatings for glass articles are numerous in both kind and purpose. The versatility of glass in recent years has caused the industry to apply coatings to glass, particularly in the form of fibers, to impart a particular physical property to the fiber. Protective coatings for glass fibers are disclosed in U.S. Pat. No. 2,444,347 to Greger et al. providing resistance to alkaline environment and to bond the fiber together. Of particular interest were glass fibers of very small diameter, termed therein "glass wool". In this form there is a large surface to volume ratio. The coating imparts some protection to the surface exposed to hostile environments. Colloidal solutions of aluminum phosphates are employed to mold glass-wool into shaped articles. The aluminum phosphates employed in the coating process are prepared in accordance with U.S. Pat. No. 2,405,884 to Greger.
Technical Bulletin I-236 published by Monsanto Company also suggests the use of colloidal aluminum phosphates as binding agents for glass fiber mats and insulation referring to the above-mentioned patent to Greger et al.
Glass fiber structures having superior heat resistance are described in Japanese Kokai No. 48 92690. According to this publication, glass fiber especially useful under elevated temperatures is provided by coating the glass fiber with a solution of aluminum phosphate or aluminum phosphate-chrome oxide complex to a thickness of from 0.1 to 10 microns. The coated fiber is heated to at least 150.degree. C. to form a uniform crystalline coating on the surface of the fiber.
Water-soluble solid aluminum phosphate complexes and binder compositions for refractory compositions or alumina are disclosed in U.S. Pat. No. 3,899,342 to Birchall et al. The complex is provided by mixing a solution of aluminum orthophosphate having an Al:P molar ratio of substantially 1:1 with anions of a carboxylic acid or a mineral oxy-acid and curing the phosphate binder at a temperature of from 80.degree. C. to 200.degree. C. or higher. Also disclosed are cold curing methods which employ a curing agent such as magnesium oxide. Cast articles are formed wherein the refractory is placed in a mold. Oxy-acids, such as citric and oxalic acids, are suggested for complexing agents with the orthophosphate.
In U.S. Pat. No. 4,147,823 to Lavalee, an ink for glass and ceramic substrates can be formulated by reacting an aluminum salt of a weak organic acid such as a stearate or palmitate with phosphoric acid to provide a matrix of insoluble aluminum phosphate cement. The complex contains filler and color pigment components which are caused to adhere to glass surfaces such as electric light bulbs. The bonding agent is heat cured at about 300.degree. C. to form an adhesively bonded mark on the glass.
Low density, high heat resistant glass fiber insulation is prepared according to Kokai No. 60-209067 to Suganuma et al. by impregnating a glass fiber needle mat with a slurry comprising an aqueous solution of an aluminum or magnesium phosphate and one or more refractory compositions such as alumina, kaolin, feldspar, etc. The glass fiber, in the form of a needle mat, is impregnated with the slurry and dried at 120.degree. C. for about one hour followed by two additional hours at 320.degree. C. to provide a molded refractory article.
A broad range of inorganic fibers are treated with a biphosphate to provide heat and flame resistance, durability and adhesion on the surface of the fibers according to Japanese Kokai No. 2-149453. Metals employed to form the biphosphate in aqueous solution are metals of Groups I, II and III of the periodic table with aluminum and magnesium preferred. The biphosphate is sprayed onto fibers, such as glass fibers, whereupon the fiber surface is partially dissolved so that the fibers are bonded in block form or bonded together providing a non-woven cloth with superior heat resistance. The biphosphate is said to be polymerized and solidified on the surface of the fiber.
Modern glass fiber insulation materials comprise very small diameter filaments and are commonly provided with organic resin coatings for several purposes. First, the brashness of glass fiber is reduced so that the amount of dust and breakage of filaments during shipping and handling is reduced. Further, glass fiber insulation is commonly supported on a substrate, such as paper or aluminum which provides, in addition to support, also insulating value. The insulation is usually prepared in a certain thickness thereby providing a desired amount of insulating value. During packaging and shipping the insulation is compressed to conserve space but when unpackaged at the location of use, the insulating material on the substrate is expected to expand so as to provide insulating value to the degree required. Another function of the organic resin coating on the glass fiber is to provide sufficient flexibility of the glass filaments such that the filaments regain most of the original thickness needed to provide the expected insulating value after packaging and unpackaging. While providing the above-described desirable results, organic resins have the possibility of contributing to environmental problems in waste disposal and in the event of combustion in the structure being insulated may emit undesired fumes. Organic resins are also combustible.
There is needed a more environmentally advantageous and effective coating for glass fiber, particularly in the insulation function where substrate support is employed. There is desired, for environmental reasons, a suitable replacement for the organic resins in glass fiber insulation.